1. Field of the Invention
The present invention relates to a proportional electro-hydraulic pressure control valve.
2. Description of the Prior Art
In the past, when measuring the line pressure or the like in a hydraulic system, it has been necessary to mount a pressure gage by a suitable pipe arrangement and directly read the indicated pressure. In this case, while no difficulty will be caused by the operation of the pipe arrangement, etc., if the necessary measures have been contemplated intentionally at the beginning of the formation of the system, in other circumstances the additional piping operation requires the investiment of additional equipment cost and operational cost. Moreover, in cases involving the use of a Bourdon pressure gage, its life has been unavoidably reduced by the surge pressure in the system and also the reduction in reliability and the occurrence of reading errors have been inevitable. Moreover, the similar inconveniences have been caused by the arrangement of a pressure detector for various control purposes.
Also, with the conventional proportional electro-hydraulic pilot relief valves and the like, the valve is used in an open-loop control which is not included in an electric feedback loop and therefore its performance is naturally limited from the structural reason of the valve, etc. For example, its repeatability and reproducibility of the hysteresis characteristics are infallibly varied due to variation in the sliding resistance of the valve and also the improvement in the response waveform of the valve to the step input is limited even if the geometrical shape of the valve and the time constant of the proportional solenoid are changed. Thus, as the usual practice in such a case, it is conceivable to perform a closed-loop control or a control which involves the mechanical parts of the valve in the feedback control loop and effect a gain adjustment, phase lag-lead compensation or the like with the aid of an electronic force thereby improving the performance. However, the construction of a closed-loop control circuit must be so large in consideration of the arrangement of a pressure detector, the wiring for its output signal, etc.